Hold off on writing the script...Unless you want to of course. 
Casper is correct. Here's a portion of the keyboard.txt file found in your userdata/settings folder.
  train_dcc_down                  x, comma
  train_dcc_up                    w, fullstop
  train_dcc_stop                  s, slash
  train_dcc_handbrake             a, apostrophe
  
  train_cabin_brake_release       q, KP9, KPPgUp
  train_cabin_brake_lap           z, KP6, KPRight
  train_cabin_brake_application   a, KP3, KPPgDn
  train_cabin_brake_emergency     pause
  train_cabin_brake_1             null
  train_cabin_brake_2             null
  train_cabin_brake_3             null
  train_cabin_brake_4             null
  train_cabin_brake_up            null
  train_cabin_brake_down          null
  train_cabin_indbrake_toggle     e, KP4, KPLeft
  train_cabin_indbrake_bail       d, KP0, KPIns
Press the A key. Z is for lap brake.
John